HERTZIAN WAVE WIFELESS TELEGEAPIIY. 559 



or inductance coils are inserted between the ends of the sensitive tube 

 and the relay and cell and serve to confine the oscillations to the tube. 



It has already been pointed out that in the transmiting aerial the 

 amplitude of the potential vibrations increases from the bottom to the 

 top, and when vibrating in its fundamental manner there is a potential 

 node at the earth connection and a potential loop or antinode at the 

 top. The same is true of the receiving aerial. Hence if the kumascope 

 employed is a Branly metallic filings tube and is inserted near the base 

 of the aerial, the difference of potential between its two ends will be 

 small. 



It has also been mentioned that a receiver of this type acts in virtue 

 of electromotive force or potential difference, and hence the proper 

 place to insert the coherer is not at the base of the aerial, but between 

 the top of the aerial and the earth. This, however, could not be done 

 by running up another wire from the earth, as that would amount to 

 putting the coherer between the tops of two identical aerials, and be- 

 tween its ends there would be no difference of potential. Professor 

 Slaby, in conjunction with Count von Arco, has given an ingenious 

 solution of this problem. If we take two equal lengths of wire, bent at 

 I'ight angles, and connect the point of intersection with the earth, 

 placing one of these wires vertically and the other horizontall}'-, we 

 tlien have an arrangement which responds to the impact of electric 

 waves, and has electrical oscillations set up in it in such fashion that 

 tlie common point of the two wires has a very small amplitude of 

 ]>otential, but the two extremities have equal and large variations. If 

 then we insert a coherer tube between the earth and the outer extremity 

 of the horizontal wire, it is influenced in the same manner as it would 

 be by the potential variations at the top of the vertical wire. In other 

 words, it is acted upon by a large difference of potential instead of a 

 small one. It is not found necessary to stretch 

 the horizontal wire out straight ; it may be coiled 

 into a spiral with open turns, and the slight 

 decrease in capacity and increase in inductance 

 resulting from this can be compensated by 

 cutting off a short piece of it 



R S 



M 





In this way we have an arrangement LLl 



/ TT -<r.\ • T • 1 J.1 J. J. -i- Fig. 19. Slaby Receiver. 



(see Fig, 19) m which the outer extremity ^, aerial = g;, earth plate -. r, 

 of this open spiral experiences variations of coherer; m, multiplier; c, 



, ,. 1 T . 1 ,1 J -ii XT condenser; /i, relay ; -B, bat- 



potential which exactly correspond with those tery; ^, earth plale. 



at the summit of the vertical aerial. The 



receiving arrangements are then completed as in Fig. 19, one end of the 

 coherer being attached to the outer end of the spiral and the other end 

 through a condenser to the earth, a relay and a voltaic cell being ar- 

 ranged as shown in the diagram. The mode of operation of tliis re- 



